1. Field of the Invention
The present invention relates to an organic EL display device, and more particularly to a highly reliable manufacturing method of an organic EL display device which suppresses the generation of dark spots or the like attributed to moisture.
2. Background Art
In an organic EL display device, an organic EL layer is sandwiched between a lower electrode and an upper electrode, a fixed voltage is applied to the upper electrode, and emission of light from the organic EL layer is controlled by applying a data signal voltage to the lower electrode thus forming an image. The data signal voltage is supplied to the lower electrode via a thin film transistor (TFT). An organic EL display device is classified into a bottom-emission-type organic EL display device in which light emitted from organic EL layers is taken out in the direction of a glass substrate on which the organic EL layers and the like are formed and a top-emission-type organic EL display device in which light emitted from organic EL layers is taken out in the direction opposite to a glass substrate on which the organic EL layers and the like are formed.
When moisture is present in an organic EL material used in an organic EL display device, the light emission characteristic is deteriorated and hence, when the organic EL display device is operated for a long time, portions of the organic EL material which are deteriorated with moisture do not emit light. These portions appear as dark spots on a display region. The dark spots grow with time and become a defect of an image. A phenomenon referred to as an edge growth in which a region where light is not emitted is increased around a pixel also occurs due to moisture.
To prevent the generation or the growth of the dark spots or the like, it is necessary to prevent the intrusion of moisture into the inside of the organic EL display device or to remove the intruded moisture from the organic EL display device. Accordingly, an element substrate on which organic EL layers are formed is sealed by a sealing substrate by way of a sealing member formed on a periphery of the element substrate thus preventing the intrusion of moisture into the inside of the organic EL display device from the outside. A sealed inner space of the organic EL display device is filled with an inert gas such as N2. On the other hand, to remove moisture intruded into the inside of the organic EL display device, a desiccant is arranged in the inside of the organic EL display device. This organic EL display device is referred to as a hollow-sealing-type organic EL display device.
The hollow-sealing-type organic EL display device has drawbacks such as difficulty in adjusting a gap between the element substrate and the sealing substrate, difficulty in adjusting pressure in the sealed inside, contamination of the organic EL material by a gas discharged from a sealing agent at the time of performing the sealing operation using a sealing agent or a low throughput. Further, there also exists a drawback that when the sealing substrate is pushed from the outside after completion of the organic EL display panel, the sealing substrate and the organic EL layer formed on the element substrate are brought into contact with each other so that the organic EL layer is broken.
To cope with such drawbacks attributed to the hollow sealing structure, there has been known a technique in which a resin sheet having a fixed film thickness is sandwiched between an element substrate and a sealing substrate thus protecting an organic EL material from moisture using such a resin sheet. This technique is referred to as solid sealing. In the solid sealing, a resin sheet is firstly adhered to the sealing substrate, and the sealing substrate to which the resin sheet is adhered and the element substrate are adhered to each other by way of the resin sheet.
The manufacture of an organic EL display panel for every individual panel is inefficient. Accordingly, there has been adopted a method in which a large mother panel on which a plurality of large-sized organic EL display panels are formed is formed, and the mother panel is separated into the individual organic EL display panels. The same goes for a liquid crystal display device. That is, there has been adopted a method in which a large mother panel on which a plurality of liquid crystal display panels are formed is manufactured, and the mother panel is separated into individual liquid crystal display panels.
With respect to the liquid crystal display device, there may be a case where a periphery of the mother panel on which respective individual liquid crystal display panels are formed is surrounded by a sealing material. This is because even when a thickness of the liquid crystal display panel is decreased due to polishing of an outer side of the mother panel, the sealing material can prevent the impregnation of a polishing liquid into the inside of the mother panel.
In this case, to separate the mother panel into the individual liquid crystal display panels, it is necessary to cut the mother panel such that cutting lines traverse the sealing material which surrounds the periphery of the mother glass on which respective individual liquid crystal display panels are formed. This cutting is performed by scribing using a diamond cutting wheel. Here, a stress generated in glass differs between a portion where the sealing material is formed and a portion which is made of only glass and hence, cross sections obtained by scribing become irregular. To prevent such irregularities in cross section, JP-A-2005-165264 (patent document 1) describes the constitution which removes the sealing material at a portion where scribes traverse the sealing material by laser beam radiation.